Diesel engines used for passenger car applications is increasing due to the benefit of better fuel economy. Further, gasoline engines are increasing compression ratios to improve the fuel efficiency. As a result, diesel and gasoline engine accessory drive systems have to overcome the vibrations of greater magnitude from crankshafts due to above mentioned changes in engines.
Due to increased crankshaft vibration plus high acceleration/deceleration rates and high alternator inertia the engine accessory drive system is often experiencing belt chirp noise due to belt slip. This will also reduce the belt operating life.
Crankshaft isolators/decouplers and alternator decouplers/isolators have been widely used for engines with high angular vibration to filter out vibration in engine operation speed range. However, although a crankshaft isolator can function very well in engine running speed range; it still presents problems during engine start-up or shut-down due to the natural frequency of the isolator itself.
Representative of the art is U.S. Pat. No. 7,507,172 which discloses a tensioner that features a backstop device which allows free rotation of the pivot arm in one direction but not the other. Reverse rotation is prevented by friction that is able to resist torque on the pivot arm under ordinary operating conditions which otherwise could permit belt tooth-skip to occur. In disclosed embodiments, the backstop device includes a stop sleeve and a clamp holder which are axially interlocked and are able to rotate relative to each other. A clutch spring surrounds permits relative rotation between the stop sleeve and the clamp holder in one direction but not the other. A clamp retained within the clamp holder frictionally engages the pivot shaft. A viscous coupling may be used in place of the frictional clamp.
What is needed is an isolating decoupler comprising a first torsion spring and a second torsion spring engaged between a spring carrier and a one-way clutch, the first torsion spring and the second torsion spring having a frictional engagement with the one-way clutch, the first torsion spring and the second torsion spring engagable with the pulley whereby upon contact with the pulley the first torsion spring and second torsion spring will release the frictional engagement with the one-way clutch. The present invention meets this need.